Device for moving a movable shaft back and forth

ABSTRACT

The device comprises a shaft provided with a drive piston movable in a gas chamber and acting as a &#39;&#39;&#39;&#39;gas spring,&#39;&#39;&#39;&#39; and a valve member and an end surface. The valve member separates two stationary chambers when on its seat. Timing means are provided which successively decrease the pressure differential which acts across said valve member and urges it toward its seat, establishing against the end surface an overpressure which forces the shaft back when the movable assembly, after having reached an end position, returns under the action of the pressure difference which has undergone a reversal across the piston and which restores onto said valve member a pressure sufficient to lock said movable assembly in rest condition.

United States Patent lnventor Antenore Pacchioni Versailles, France Appl, No. 801,425 Filed Feb. 24, 1969 Patented Feb. 9, 1971 Assignee Commissariat A LEnergie Atomique Versailles, France Priority Feb. 29, 1968 France PV 14 1858 DEVICE FOR MOVING A MOVABLE SHAFT BACK AND FORTH 4 Claims, 3 Drawing Figs.

US. Cl 91/35 Int. Cl FlSb 21/02 Field ofsearch 91/5, 35,

[56] References Cited UNITED STATES PATENTS 3,336,788 8/1967 )ttestad et a]. 91/5(X) 3,352,143 11/1967 Bollar 9l/5(X) 3,412,645 11/1968 Kirk 9l/393(X) Primary ExaminerEverette A. Powell, Jr. AttorneyCraig, Antonelli, Stewart and Hill ABSTRACT: The device comprises a shaft provided with a drive piston movable in a gas chamber and acting as a gas spring, and a valve member and an end surface. The valve member separates two stationary chambers when on its seat. Timing means are provided which successively decrease the pressure differential which acts across said valve member and .urges it toward its seat, establishing against the end surface an .overpressure which forces the shaft back when the movable assembly, after having reached an end position, returns under the action of the pressure difference which has undergone a reversal across the piston and which restores onto said valve member a pressure sufficient to lock said movable assembly in rest condition.

FIG. '2

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SHEET 3 UF 3 INVENTOR A TINOIE PACLHI'ONI M M M v KL ATTORNEE DEVICE FOR MOVING A MOVABLE SHAFT BACK AND FORTH The present invention is directed to a device for producing high-speed reciprocating motion and especially for actuating the moving system of a bubble chamber of large size.

Bubble chambers, which rank among the most powerful instruments of fundamental research in the field of high-energy particle physics, comprise a vessel which contains a liquid such as liquid hydrogen. As a result of sudden expansion, the temperature of the liquid falls below the boiling point, whereupon the passage of each particle is indicated by a train of bubbles which can be photographed. The expansion is usually produced by displacement of a piston either at the top of the liquid or within flask which is separate from the bubble chamber proper but which is connected to the top of the chamber by means of a row of parallel tubes, the total junction cross section being sufficient to ensure that the pressure drop within the top fhsk propagates to the bubble chamber without undue loss of pressure.

The moving system which comprises the expansion piston must be subjected to an extremely rapid movement of displacement during a single expansion cycle. However, in large bubble chambers, this moving system has a very high inertia and the actuating device must ensure a very rapid rate of operation in order to derive full advantage from the possibilities offered by high-power particle accelerators. Under these conditions, there is no question of dissipating the energy applied to the moving system as each back-and-forth movement takes place and an expedient must be found for building up and restoring this energy: a solution is described in French Pat. No. 1,464,077 filed by Commissariat a lEnergie Atomique; however, one objection to the device according to the patent cited is that movable latching arms are employed for the purpose of retaining the moving system in its rest position are liable to wear while said position must in addition be defined with precision. The primary object of the present invention is to remove this disadvantage while also providing a control system which entails only a small consumption of driving fluid as each back-and-forth movement takes place.

With this objective, the invention proposes a device for producing high-speed reciprocating movements, especially for bubble chambers, of the type comprising a piston which forms part of the moving system to be displaced and which divides into two substantially leak-tight compartments a first space defined by a stationary casing, and means for establishing within one of the two compartments a pneumatic pressure which is higher than the pressure developed within the other compartment, said device being especially characterized in that it also comprises:

a valve body which forms part of said moving system and defines the rest position of the moving system by coming up against a valve seat provided in said casing and accordingly dividing into two compartments a second space which is defined by the casing;

a plunger which is rigidly fixed to the moving system and has a surface which'defines a latching cavity with the stationary casing;

an extension of said plunger which is adapted to move within a passage providing a communication between a control space of said casing and the latching cavity and which constricts said passage when the moving system is in the rest position;

synchronization means for successively reducing a pressure which produces action on the valve body so as to apply this latter against its seat; and

the production within said control space of an overpressure which produces action on the plunger through the intermediary of the passage when the moving system, after reaching an end position, has returned backwards under the-action of the pressure difference which has reversed between said two compartments and the restoration of the pressure on the valve in order to relatch the moving system in said predetermined rest position.

A better understanding of the invention will be gained from the following description of one embodiment of the invention which is given by way of example and not in any sense by way of limitation, reference being made to the accompanying drawings, in which:

FIG. 1 shows diagrammatically the device for actuating the piston of a bubble chamber as shown in cross section along a plane which passes through the vertical axis of displacement in the rest position.

FIG. 2, which is similar to FIG. I, shows the components of the device in the position occupied by these latter when the moving system of the device reaches the bottom position on completion of its resilient back-and-forth movement before energy is supplied from the exterior.

FIG. 3 is a diagrammatic sectional view of a bubble chamber taken along a plane which passes through the vertical axis of displacement of the expansion piston.

The bubble chamber which is illustrated in FIG. 3 comprises a chamber A of generally spherical shape having a horizontal axis at right angles to the plane of the FIG. and provided with viewing windows 6. Said chamber is provided with extensions in the form of a series of vertical ducts 8 located in the vertical plane which passes through the axis of the cylinder, only one of said ducts being shown in FIG. 3. The ducts 8 open into a vessel 10 having a vertical axis and comprising a cylindrical portion 12 in which an expansion piston 14 is slidably mounted. Leakages exist between the cylindrical portion 12 and the piston 14 but they are of sufficiently small value not to cause undue attention of the pressure drop which is produced by the rapid upward motion of the piston.

The expansion piston 14 is associated with a moving system which is shown in FIG. 1. This moving system comprises a shaft 16 which is attached to the expansion piston. The shaft 16 is advantageously designed in two sections which are coupled together by means of a joint consisting of semicircular flanges 19 and bolts.

A space which is defined by a stationary casing 20 formed of a number of interassembled parts is divided by the piston 18 into a lower compartment 22 and an upper compartment 24 which are essentially leak tight. When the drive piston 18 takes up the position in which it is shown in FIG. 2, pressurized gas is introduced into the compartments 22 and 24 by means of pipes 26 and 28, the pressure within compartment 22 being considerably higher than in compartment 24. The pipes referred to are then closed off, their only remaining function being to readjust the pressures at long time intervals. It is possible, for example, to employ nitrogen as filling gas at a pressure of bars (2,310 p.s.i.) in compartment 22 and at a pressure of 60 bars (870 p.s.i.) in compartment 24.

The pressure difference within the compartments 22 and 24 exerts on the piston 14 a force which tends to drive this latter upwards. The rest position of the moving system is defined by the abutting application of a valve 32 which is integral with the shaft 16 against a leak-tight seat 30 which is carried by the casing. When the valve is applied against the seat 30, a space which is formed within the casing is consequently divided into two leak-tight compartments 34 and 36. A pipe 38 continuously supplies the compartment 34 with hydraulic fluid at high pressure and a second pipe 40 provides a communication between the compartment 36 with an electrovalve 42 having a plurality of passageways which serve to connect said compartment either to the supply of hydraulic fluid at high pressure or to the discharge pipe 44. In the second case, the hydraulic pressure forces exerted on the valve balance the action of the pressure difference which acts on the piston 18 and retain the moving system in the rest position shown in FIG. 1.

, A downwardly directed impulse can be exerted on the end face 46 of the shaft 16 which defines with the casing a relatching cavity 48. A passage which can be sealed off by means of a valve 52 provides a communication between the top portion of said cavity and a compensation chamber 50. The chamber 50 is connected to the discharge duct 44 by means of a pipe section in which is formed a constricted portion 53. The valve 52 is adapted to slide with slight friction within a stationary body 54 which is joined to the casing by means of ribs 56. A small piston 58 to which a low pneumatic pressure is applied by means of a pipe 59 forces the valve 52 downwards, namely towards the open position thereof. Closure of the valve 52 is effected by increasing the pressure applied against the rear valve face which defines a chamber 60 with the stationary body 54. Said chamber 60 is connected on the one hand to a three-way electrovalve 62 which makes it possible either to supply the chamber with hydraulic fluid at high pressure or to connect said chamber to the discharge pipe 44; said chamber also communicates continuously with the cavity 48 via a calibrated passage 64. A rod 66 which is attached to the shaft is capable of displacement within said passage and has a variable diameter so that the passage cross section between the chamber 60 and the cavity 48 is progressively constricted when the shaft moves from the uppermost position (in chain-dotted lines in FIG. 2) to the rest position (shown in FIG. 1).

In order to prevent leakage of hydraulic fluid from disturbing the operation of the valve 52, said leakage is collected in an annular space 68 which is connected to the discharge by means of a pipe 70. In addition, the compensation chamber 50 is separated from a pneumatic compartment 76 by means of a sliding separator 72 which is fitted with seals. A pipe 74 serves to establish within the compartment 76 a low pneumatic pressure which is sufficient to maintain the separator 72 at rest in the bottom position thereof (as shown in FIG. 1) and in contact with the oil while the movement takes place.

The electrovalves 42 and 62 are controlled automatically by means of a conventional synchronization device. The means adopted for this purpose can consist, for example, of the electronic device 78 which is illustrated in FIG. 1. This device comprises a clock 80 which, when a drive signal is applied thereto by a pulse generator 82, delivers at two outputs in alternate sequence a train of pulses which are spaced at predetermined time intervals. There can be employed, for example, a decatron time-base which delivers 12 pulses having a spacing which varies from to 1 second in steps of sec. The outputs of the clock are coupled to flip-flops 86 and 88 which control the electrovalves 42 and 62 (indicated in chaindotted lines in FIG. I).

The operation involved in the initiation of a rapid reciprocating movement of the moving system (upward movement followed by a downward movement) will now be briefly described.

When the device is set, its components occupy the positions shown in FIG. 1. A high pressure (160 bars or 2,320 p.s.i., for example) is maintained in the compartment 22 and a lower pressure (of 60 barsor 870 p.s.i., for example) is maintained in the compartment 24. The volume of the compartment 22 is slightly smaller than the volume of the compartment 24. The valve 52 is in the bottom position thereof. The electrovalves establish the connections indicated by the arrows f and f (FIG. 1). The shaft 16 is retained in the bottom position as a result of the pressure difference between the chambers 34 and 36. The high hydraulic pressure must obviously have a value such that the retaining force exerted on the valve 32 is slightly higher than the force exerted on the piston 18.

Triggering is carried out by connecting the compartment 36 to the supply of hydraulic fluid under pressure and injecting fluid into said compartment. The synchronization device 78 is accordingly put into operation for this purpose. The generator 82, which is actuated, for example, by establishing the magnetic field within a particle accelerator, triggers the clock 80 at the instant t At the instant t t 6 t, the clock applies to the flip-flop 86 a drive pulse which causes this latter to change over to its second state and delivers to the electrovalve 42 a switching signal which establishes a communication between the compartment 36 and the high-pressure fluid supply.

The balance of forces is upset, the shaft moves upwards and the valve 32 is lifted, thereby equalizing the pressures within the compartments 34 and 36 almost instantaneously without entailing any need of a substantial supply of liquid through the pipe 40 The downwardly directed force which is exerted on the valve 32 is reduced to zero and the pressure of the gas contained within the lower compartment 22 thrusts the moving system upwards. During this movement, the total volume of hydraulic fluid which is present within the compartments 34 and 36 does not change whilst the hydraulic fluid contained in the cavity 48 is forced up into the chamber 50 and lifts the separator 72. In regard to the fluid which is present within the chamber 60, said fluid passes out in the direction of the arrow f towards the discharge pipe 44. Since the volume displaced by the rod 66 is relatively small, the braking action produced by the hydraulic fluid as this latter passes out of the compartment 60 is not of significant magnitude.

The moving system thus performs its upwards range of travel whilst the pressures within the compartments 22 and 24 are reversed. Thereupon, the moving system returns downwards under the action of the downward force exerted on the piston 18.

At a suitably chosen instant 1 corresponding to the end portion of the return travel of the moving system, it is necessary to apply an additional downward impulse to the moving system: the clock changes the state of the flip-flop 88. Said flip-flop then delivers a signal for switching the electrovalve 62 so as to connect the chamber 60 to the source of hydraulic fluid under pressure (arrow f l in FIG. 2). The hydraulic fluid under high pressure penetrates into the chamber 60. Since the moving system is still located above the rest position, the rod 66 leaves a passageway of relatively large cross-sectional area between the chamber 60 and the cavity 48: the pressure drop which is caused by the constriction of the fluid which flows in the direction f2 must nevertheless be of sufficient magnitude to lift the valve 52 and cut off the communication between the chamber 50 and the cavity 48. The hydraulic fluid which is admitted into the cavity 48 which is thus closed increases the pressure within said cavity and applies to the end face 46 a force which tends to thrust the shaft 16 downwards. The work performed by this force compensates for energy losses during the back-and-forth motion of the piston 18 and gives the moving system an additional impulse which is intended to apply this latter in abutting contact with the seat 30. During the final stage of approach of the valve 32 towards its seat, the enlarged portion of the rod 66 throttles the passage 64, retards the admission of hydraulic fluid into the cavity 48 and slows down the moving system, thereby reducing the force of impact of the valve 32 against its seat 30.

When the valve has just been applied against its seat, a pulse delivered by the clock 80 at an instant t changes the state of the flip-flop 86 and switches the electrovalve 42. Thus, the compartment 36 which is again isolated by the valve 32 is connected to the discharge pipe 44. A pressure-induced force is exerted on the valve and maintains this latter in the rest position.

Finally, at the instant t, which follows t;,, a further pulse from the clock 80 changes the state of the flip-flop 88 and switches the electrovalve 62 so as to connect the chamber 60 once again to the discharge pipe 44: the valve 52 opens under the action of the small piston 58, the excess hydraulic fluid which is admitted by the electrovalve 62 into the cavity 48 flows through the constricted portion 53 towards the discharge pipe and the device is in readiness for a further sequence of operation.

It is clear that the device which has been described in the foregoing has a large number of advantageous features. Thus, a small quantity of hydraulic fluid (usually a few cubic centimeters) is sufficient to release the substantial energy which has built up in the form of compressed gas within the compartments 22 and 24, thereby constituting a pneumatic spring. By virtue of the small volume of hydraulic fluid which is expended, it is only necessary to utilize a low-power compressor. Inasmuch as the hydraulic fluid has a very low degree of compressibility, the electrovalves which constitute the only movable control elements can be located at a distance from the device. The device itself is of very rugged design, especially by virtue of the fact that there are no delicate moving parts.

It is evident that the invention is not limited to the form of construction which has been described in the foregoing solely by way of example and that the scope of this patent extends to alternative forms.

lclaim:

l. A device for moving back and forth at high speed a movable shaft provided with a piston which separates a space delimited by a stationary easing into two substantially pressure tight compartments, with a valve member which sealingly abuts a stationary seat and separates two chambers when said device is in rest condition, with a surface transverse to the axis of the shaft and which constitutes a movable wall of a locking chamber and with a projection which is movable in a passage connecting said locking chamber and a drive chamber and which throttles said passage when in rest condition, comprising means for establishing a pressure difierential between said compartments which exerts on said piston a force in a direction which biases said valve member away from its seat when in rest condition, and timing means for sequentially decreasing a pressure differential which normally acts across said valve member and maintains it in seated condition, for establishing within said drive chamber an overpressure which is communicated to said locking chamber and biases said radial surface while the movable assembly, after having reached an end position, returns under the action of the pressure differential which has undergone a reversal between said two compartments and for restoring onto said valve member after it has been returned to its seat a pressure sufficient to lock said movable assembly in rest condition.

2. A device according to claim 1, wherein said shaft carries an expansion piston disposed within a vessel which is in communication with a bubble chamber.

3. A device according to claim 2, having an opening closable by a second valve member and which connects said locking chamber with a compensation chamber connected to discharge by a throttled line, means permanently and resiliently biasing said second valve member toward its open condition, said second valve member being subjected to the pressure prevailing in the drive chamber whose increase urges it to its closed condition.

4. A device according to claim 3, wherein opposed faces of said second valve member are respectively subjected to the pressure prevailing in said locking chamber and to the pressure in the drive chamber and wherein said projection is so shaped as to throttle the communication between the drive chamber and the locking chamber when in or closed to rest condition, whereby upon admission of pressurized fluid into said drive chamber by said timing means, the pressure difference due to head loss-through said communication urges said second valve member to its closed condition against the action of the resilient means. 

1. A device for moving back and forth at high speed a movable shaft provided with a piston which separates a space delimited by a stationary casing into two substantially pressure tight compartments, with a valve member which sealingly abuts a stationary seat and separates two chambers when said device is in rest condition, with a surface transverse to the axis of the shaft and which constitutes a movable wall of a locking chamber and with a projection which is movable in a passage connecting said locking chamber and a drive chamber and which throttles said passage when in rest condition, comprising means for establishing a pressure differential between said compartments which exerts on said piston a force in a direction which biases said valve member away from its seat when in rest condition, and timing means for sequentially decreasing a pressure differential which normally acts across said valve member and maintains it in seated condition, for establishing within said drive chamber an overpressure which is communicated to said locking chamber and biases said radial surface while the movable assembly, after having reached an end position, returns under the action of the pressure differential which has undergone a reversal between said two compartments and for restoring onto said valve member after it has been returned to its seat a pressure sufficient to lock saiD movable assembly in rest condition.
 2. A device according to claim 1, wherein said shaft carries an expansion piston disposed within a vessel which is in communication with a bubble chamber.
 3. A device according to claim 2, having an opening closable by a second valve member and which connects said locking chamber with a compensation chamber connected to discharge by a throttled line, means permanently and resiliently biasing said second valve member toward its open condition, said second valve member being subjected to the pressure prevailing in the drive chamber whose increase urges it to its closed condition.
 4. A device according to claim 3, wherein opposed faces of said second valve member are respectively subjected to the pressure prevailing in said locking chamber and to the pressure in the drive chamber and wherein said projection is so shaped as to throttle the communication between the drive chamber and the locking chamber when in or closed to rest condition, whereby upon admission of pressurized fluid into said drive chamber by said timing means, the pressure difference due to head loss through said communication urges said second valve member to its closed condition against the action of the resilient means. 